1. Field of the Invention
This invention relates to a graft copolymer having an organopolysiloxane grafted onto a trunk polymer comprising a vinyl chloride/vinyl alcohol copolymer, and a coating composition composed mainly of the graft copolymer.
2. Description of the Prior Art
Vinyl chloride/vinyl alcohol resins having vinyl chloride and vinyl alcohol as constituent monomer units have such advantages (1) that they form coated films excellent in toughness, flexibility and flame retardancy, (2) that they form coated films excellent in alkali resistance, oil resistance and chemical resistance, (3) that they are well compatible with other resins for coated films, particularly alkyd resins, (4) they are excellent in solubility in solvents, etc., and therefore have been used for various uses, including intermediate painting for ship paints, metal protective paints, wood paints, metal finishing paints, binder resins for recording medium, resins for being mixed into alkyd resins, etc. In such vinyl chloride/vinyl alcohol resins, for the purpose of imparting further special functions such as slippage, water repellency, mold release, etc., addition of silicone oils has been investigated in the prior art.
However, since dimethyl silicone oil has no compatibility with vinyl chloride/vinyl alcohol resins, if it is added to said resin, there have been involved such drawbacks that the film became turbid, or the surface characteristics were worsened. On the other hand, when a silicone oil improved in compatibility by modification with the pheyl group, a long chain alkyl group, polyoxyalkylene, etc. is added, although the above drawbacks can be cancelled, there has been involved the drawback that the effects such as mold release, slippage or water repellency cannot persist. Accordingly, in order to improve durability of the mold release, etc., there has been also made an attempt to add a reactive silicone oil having reactive group such as ##STR1## etc. which react with hydroxyl groups of polyvinyl chloride resins. But in this case, there is a problem in pot-life of the resin obtained, or addition of a catalyst or heating was required, whereby the use range was disadvantageously limited.